Possession of multiple cilia and flagella bestows significant evolutionary advantage upon living organisms
only if these organelles can achieve coordination.
This may be for purposes of swimming [1]}, [2]}, feeding [3]}, or fluid
transport [4]}, [5]}.
Multiciliation may have evolved first in single-celled microorganisms due to the propensity for hydrodynamic
interactions to couple their motions, but was retained in higher organisms, occurring in such places as
the murine brain [6]} or human airway epithelia [7]}.
Since Sir James Gray first noted that “automatic units” of flagella beat in “an orderly sequence” when placed
side by side [8]}, others have observed the tendency for nearby sperm cells to undulate in unison or aggregate
[9]}, [10]}, and subsequently the possible hydrodynamic origins of this
phenomenon have been the subject of extensive theoretical analyses [11]}, [5]}, [2]}.
Despite this, the exclusiveness and universality of hydrodynamic effects in the coordination of neighboring cilia and flagella
remains unclear.
